First, I’m not an electronics engineer, just a hobbyist.
Second, a 2N3904 is NPN, and a 2N4058 is PNP. So right there something’s completely wrong. One cannot replace the other.
Same thing for 2N3906 (PNP) replacing a 2N3392 (NPN).
Are you sure you didn’t get mixed-up when flipping the circuit around ? Because a 2N3904 can replace a 2N3392 (Q14) and a 2N3906 can replace a 2N4058 (Q24).
Although, as you said, ideally Q14 should be matched with Q23 (connected as a current mirror).
Q24 is part of the glide circuit as its collector pin is going to the glide pot (thru R61). And Q14 is also receiving the output of the glide circuit on its base pin (from the Signal pin of FET transistor Q10) thru R30.
Yeah, you’re right, I’m just confused! The 3392 is replaced with the 3904.
And you’re obviously right that the transistors in question interact.
This is the point were my highly limited electronics skills always fail me - I can often figure out that “this part of the circuit is an amplifier, that part is a flip-flop” etc, but I can’t figure out how they interact.
You may be just a hobbyist, but I’ve read a lot of your posts and compared to me, you’re an expert!
Now I’ll just have to find a source for 3392’s (or equivalents), get a bunch and try to match a pair…
As long as their legs are the same length that means that they’re matched…
Nah, just kidding.
Don’t worry, when I read the description of the glide circuit, explained in great details in the Minimoog D service manual (on page 16 in the pdf version), I get a little lost also.
As for matching transistor, it’s not that difficult with a good, precise multimeter. It’s also described in the service manual on page 63 in the pdf version.
Your glide problem could be caused by a failed FET transistor in the glide circuit.
Yeah, I’ve read the service manual and the service notes. Again, and again, and again…
I was hoping this was a well known issue, so I wouldn’t have to source too many hard-to-get components. And the best match I’ve found for the FET’s is Iabout $10 each. Ouch! But I guess it’s not a bad thing to have some spare parts around, so I’ll try to get them all.
But I do think I’ve seen a Youtube vid with a guy demoing a mini that had the same issue. He didn’t mention it as an issue - in fact, I got the impression he thought the behaviour was by design. But there was a comment saying “my glide doesn’t change the pitch like that”. Gonna have to try to find that vid again. Maybe the guy figured out the issue and solved it. Or maybe it’s his mini that’s now in my possesion…
